Root canal shaping is an essential component to endodontic therapy. The principle here is to enlarge the main canal to allow subsequent irrigation with disinfecting solutions to be efficient. It is desirable to enlarge without thinning or weakening the canal walls, since one of the potential unfavorable outcomes of root canal treatment is vertical root fracture.
Nickel-titanium root canal instruments have generated a significant change in the way root canal treatments are performed today. They are very reliable adjuncts in endodontic therapy; however, their mechanical characteristics are still poorly understood. Specifically, NiTi instruments do fracture more often than conventional stainless-steel K-files.
Two main fracture modes have been identified through which these fractures occur: torsional fracture, whereby the tip of the rotary becomes wedged into a small canal cross-section and snaps, and fatigue failure, whereby repeated compression and elongation of metal ultimately leads to work hardening and brittle fracture.
The current opinion is that handling parameters, such as rotational speed, number of usages and the lubrication medium, play important roles in the performance of NiTi rotaries. One current project has tried to quantify this opinion with a Web-based questionnaire.
From the data gathered so far, it appears that more in vitro tests are needed to allow clinicians to select the most appropriate parameters clinically. We developed a torque-testing platform that enables objective tests of the behavior of root canal instruments under simulated clinical conditions. It assesses parameters including torque, apical force, cutting efficiency and cyclic fatigue. Current and planned future projects involve new instrument designs and material choices, as well as instrument sequences.